The present invention relates generally to welding systems and, more particularly, to a welding system configured to automatically adjust a wire feed speed to quickly and consistently generate stable welding arcs.
During a welding process, a filler material, or wire, is typically introduced to a workpiece. A power source generates an electrical signal that results in an electrical potential between the workpiece and the filler material when a separation is maintained therebetween. This electrical potential generates an arc between the filler material and the workpiece that then generates a weld pool. As the arc is initiated, if the filler material cannot support the electrical potential, a section of the filler material may collapse. Conversely, if the electrical potential is insufficient to liquefy a portion of the filler material to generate the weld pool, a short circuit condition can develop between the filler material and the workpiece that will result in the base of the arc as the filler material contacts the workpiece. As such, the parameters of the weld power signal and the rate of delivery of filler material directly effect weld arc generation and the quality of the starting arc.
Wire feeders are typically used to feed the filler material, generally a metal wire, into a weld during a welding process, such as Gas Metal Arc Welding (GMAW) or other welding processes. Typical wire feeders have a drive roller assembly for driving the metal feed from a feed spindle through a welding gun for introduction to the weld. Power is supplied to the drive roller assembly by a welding power supply via a weld cable. The speed in which the metal filler material is fed to the weld is known as the “wire feed speed” (WFS), and can be selected by an operator of the welding device who presets the WFS to a desired wire feed speed. In other processes, the WFS can be adjusted to maintain a constant parameter, such as in constant voltage (CV) welding, constant current (CC) welding, or constant voltage-constant current (CV-CC) welding. Typically, the WFS is adjusted based on the thickness of the metal being welded, a wire deposition rate, a desired material transfer mode, and desired weld power parameters such as a weld voltage or a weld current. The WFS is set to perform a desired welding application.
During a given welding process, if the welding arc is underpowered, the weld strength can be insufficient to adequately join the materials being welded. On the other hand, if the welding arc is overpowered, it is possible to “burn through” the materials being welded. Between these two extremes there is a range of power settings and wire feed speeds where welding can be performed, but may not have a preferred arc characteristic. That is, if the power and feed speed result in a slightly underpowered welding arc, the welding process can repeatedly arc and short as the wire touches the work piece resulting in a spattered weld. Alternatively, if the power and feed speed result in a slightly overpowered weld, the welding arc can repeatedly be formed and collapse as extended sections of weld wire are prematurely introduced into the weld, resulting in poor consistency. A weld produced with either the overpowered or underpowered arc characteristics can have varying degrees of poor weld quality in strength and/or aesthetics, inefficient power usage, and overall reduced operation efficiency.
Various known welding techniques have attempted to address the issue of stable weld arc generation, or arc starts, with mixed results. One such technique requires using a motor with retract capabilities, touching the wire to the workpiece, retracting to initiate an arc, and then feeding wire back into the weld after the start is completed. This technique substantially increases system complexity by requiring a fast retract motor and associated circuitry. It is also generally slower as it requires substantial changes in both wire feed direction and repeated wire feed speed accelerations and decelerations. Other techniques provide for adjusting the power, voltage, or current supplied to the weld from a power source during arc starts. These techniques monitor voltage and/or current at the weld and adjust the amount of voltage or current provided thereto in an attempt to better control the arc characteristics. Other techniques provide a means for retracting the wire once an arc is detected. Because these systems directly control the power signal provided to the weld, they must be relatively robust to support and manipulate the power signal required for welding processes. The robust nature of the control system increases assembly, repair, and manufacture costs by requiring a device having additional components and circuitry as well as increasing the overall complexity of the device.
It would, therefore, be desirable to have a system and method capable of generating a stable welding arc that is relatively simple in construction and efficient in operation.